摘 要：
A comparative study has been made of the typical rice bacterial leaf blight
organism (cultures OS-2 and OS-6) with the bacterial leaf streak organisms of rice
(cultures O-300,O-27 and O-1) and Leersia hexandra Swartz.(cultures G-2 and G-
12) from Kwangtung.
Seven cultures compared were found similar in morphology,but different in
cultural characteristics,physiological and biochemical properties,serological reactions
and pathogenicity.They are separated into three groups.
Cultures OS-2 and OS-6 were shown by artificial inoculations to produce typi-
cal symptoms of rice leaf blight first described by Japanese workers,and were found
to be identical bacteriologically with the original descriptions of Ishiyama.Con
sequently,the leaf blight organism of rice occurring in Eastern and Central China
can be identified as Xanthomonas oryzae (Uyeda and Ishiyama) Dowson.
Cultures O-300,O-27 and O-1 when artificially inoculated on the leaves of rice,
produced water soaked streaks with large amount of bacterial exudate and the symp-
toms were identical with those found under natural conditions in Kwangtung.They
are different from Xanthomonas oryzae in pathogenicity and other bacteriological
characters.The bacterial leaf streak of rice in Kwangtung is an entirely different
disease and the causal organism is identified as a new bacterial plant pathogen:
Xanthomonas oryzicola n.sp.Rods,1.2×0.3-0.5μ,single,occasionally in pairs but
not in chains;no spores and no capsules;motile by a single polar flagellum.Gram
negative.Aerobic,grow favorably at 28℃.Colonies on nutrient agar pale yel-
low,circular,smooth,margin entire,convex and viscid.Growth on slant filiform.
Growth on nutrient broth moderate,surface growth ring form but no definite pel-
licle.No growth on Cohn's and Fermi's solution.Gelatin liquefied,milk not coa-
gulated but peptonized,reaction of litmus slightly alkaline and litmus mostly
reduced.Nitrites not produced from nitrates;hydrogen sulphide and ammonia
produced;no indole.Acid but no gas from dextrose,sucrose,xylose and mannose;
no acid from lactose,maltose,arabinose,mannitol,glycerol and salicin.Starch
not hydrolyzed.Methyl red and V.P.tests negative.Pathogenic to rice by
producing water soaked streaks which expand to form yellowish brown streaks or
stripes with large amount of bacterial exudate.Weakly pathogenic to Leersia he
xandra,producing small purpurish spots or narrow stripes on leaves by artificial
inoculations;not pathogenic to Zizania latifolia Turez.
Cultures G-2 and G-12 isolated from Leersia hexandra in Kwangtung were found
different both from the leaf blight and the leaf streak organism of rice.They were
shown to be weakly pathogenic to rice by artificial inoculations and would not pro
duce leaf blight or leaf streak if the matured plants of rice were inoculated by spray-
ing with the bacterial suspensions of the respective cultures.Although they are
more or less similar to the rice leaf streak organism in physiological and biochemi
cal reactions,yet considering their difference in pathogenicity,cultural characters
and serological reactions,the causal organism of the bacterial leaf streak of Leersia
??hexandra is also identified as a new species:Xanthomonas leersiae n.sp.Rods,
1.2-1.4×0.4μ,single,occasionally in pairs but not in chains;no spores and no cap
sules;motile by a single polar flagellum.Gram negative.Aerobic,grow favorably
at 28℃.Colonies on nutrient agar waxy yellow,circular,smooth,margin entire,
convex and very viscid.Growth on agar slant filiform.Growth on nutrient broth
moderate,surface growth ring form but no definite pellicle.No growth on Cohn's
and Fermi's solution.Gelatin rapidly liquefied,milk not coagulated but peptonized;
reaction of litmus slightly alkaline and litmus mostly reduced.Nitrites not produced
from nitrates;hydrogen sulphide and ammonia produced;no indole.Acid but no
gas from dextrose,sucrose,xylose,mannose and arabinose;no acid from lactose,
maltose,mannitol,glycerol and salicin.Starch not hydrolyzed.Methyl red and V.
P.tests negative.Pathogenic to Leersia hexandra,producing water soaked streaks
with bacterial exudated on leaves;weakly pathogenic to rice as shown by artificial
inoculations.Not pathogenic to Zizania latifolia Turez.
The work was confirmed by the South China Agricultural College and the South
China Agricultural Research Institute with similar experiments made on cultures
OS-2,O-27,O-300,O-242,O-777,O-842,G-12,G-166,G-295,57-G-42 and 57-G-65.
Results of experiments failed to demonstrate that Leersia spp.(Leersia hexandra
Swartz.and L.japonica Makino) are the natural hosts of the leaf blight organism (X.
oryzae).The relation between the streak organism of rice and Leersia hexandra is
still not clear.Results of artificial inoculations made in South China demonstrated
that several isolates from Leersia hexandra were quite virulent to rice,but the ex-
periments could not be repeated in Nanking.It needs further investigations.
